Effect of hydrogen on the Young's modulus of iron

A Bordoni type apparatus was used to measure the change of the apparent Young's modulus ofα-Fe induced by hydrogen. The solution of the flexural vibration equation of a beam under stress indicatesE = C(σ)ω ². If the resonant frequencies of the first and the third tone are measured at about the same time,E andσ can be calculated. The change of the apparent Young's modulus after charging with hydrogen is defined as ΔE = ΔE ₁(H) + ΔE ₂, where ΔE ₁(H) relates to the change of the perfect crystal interatomic cohesive force and ΔE ₂ is induced by the change of stress. An artificially partial stress relaxation test was carried out to measure ΔE ₂. The results show that during aging, after both charging with hydrogen and artificial stress releasing, the change of the apparent modulus is the same,i.e., ΔE = ΔE ₂. Thus, the ΔE ₁(H) associated with the interatomic cohesive force does not evidently change during aging with escaped hydrogen of 7 to 8 wppm at room temperature,i.e., this amount of hydrogen does not decrease the interatomic cohesive force ofα-Fe.     

The influence of hydrogen on atomic binding energy,critical slip shear stress,and fatigue crack propagation rate of aluminum single crystals

The critical slip shear stress of pure aluminum (99.999. pet) single crystals was reduced after hydrogen-charging. The atomic binding energy of aluminum was studied with a secondary ion microprobes mass analyzer, and it was found that this binding energy was reduced about 11 pct after hydrogen-charging. These two effects were used to explain the fact that the fatigue crack propagation rate of pure aluminum single crystals was accelerated after hydrogen-charging.     

Fibrin-Based Drug Delivery Systems. II. The Preparation and Characterization of Microbeads

An emulsion method was employed to prepare fibrin beads having different sizes in this study. The oil phase of emulsion system was consisted of mineral oil with various amount of oleic acid as surfactant. Fibrin was converted from fibrinogen with thrombin in Tris buffer solution, then the mixture was emulsified into the oil phase forming droplets. After curing for one hour, 400 ul of glutaraldehyde solution (0.5% v/v) was added to minimize coagulation. The recovery of fibrin beads was simply done by decanting the oil phase and washing the residual with diethyl ether once and then with a mixture of isopropanol and n-hexane (1:3) containing 0.2% w/v Tween 80 twice. As expected, increasing the amount of oleic acid in the oil phase decreased the size of fibrin beads. It is due to the decrease of interfacial tension with increasing oleic acid amount. The presence of macromolecules showed no interference on the formation of fibrin beads except lysozyme. The diffusion characteristics of fibrin beads was evaluated using macromolecules of different molecular weight as model. The size of fibrin beads affected the penetration rate, whereas the effect of molecular weight of macromolecules was inconclusive. An exponential equation was able to approximate the penetration of macromolecules into fibrin beads during the late-time period. The possibility of using fibrin beads as the carrier to deliver protein drugs was appreciated.     

Workforce considerations: maintenance of the future ATC system

The authors describe the development of a remote maintenance monitoring system, the rationale for consolidation of the field maintenance workforce, and the development of an automated modeling tool, the work center consolidation model. The model is described, and the methodology used to validate a node substitution algorithm is explained in detail. The node substitution algorithm has been implemented and incorporated into the work center location model (WCLM). The improved WCLM has the combined benefits of the dBASE III command language and the reduced processing requirements of the node substitution algorithm. This provides user friendliness and fast and flexible data manipulation, while the node substitution algorithm allows the WCLM to model regionwide problems in reasonable time and with reasonable effort. The improved WCLM has been successfully used to model the US Federal Aviation Administration (FAA's) Southern Region. The WCLM was able to model the various configurations required by the region, and it produced the optimal combination of work centers acceptable to the region     

Interactive repair assistant: A knowledge-based system forproviding advice to field technicians

The IRA (Intelligent Repair Assistant) expert system is described. This system is used to assist mobile field technicians who are repairing circuits and having noise and transmission problems. It is shown how artificial intelligence techniques can be used by using software tools that are common to the application but not necessarily suited to artificial intelligence. It is stressed that integrating the expert system within the operational environment is a crucial factor in choosing the appropriate software tool